Random access procedures for link budget constrained wireless devices

ABSTRACT

This disclosure relates to accommodating link budget constrained wireless devices performing random access procedures. A base station may detect a preamble message from a wireless device. It may be determined that the preamble message is received from a link budget constrained wireless device. Characteristics of a response message may be selected based at least in part on determining that the preamble message is received from a link budget constrained wireless device. The response message may be transmitted to the link budget constrained wireless device using the selected characteristics.

PRIORITY INFORMATION

This application claims priority to U.S. provisional patent applicationSer. No. 62/173,773, entitled “Random Access Procedures for Link BudgetConstrained Wireless Devices,” filed Jun. 10, 2015, which is herebyincorporated by reference in its entirety as though fully and completelyset forth herein.

FIELD

The present application relates to wireless devices, including tosystems, apparatuses, and methods for link budget limited wirelessdevices to perform random access procedures.

DESCRIPTION OF THE RELATED ART

Wireless communication systems are rapidly growing in usage.Additionally, there exist numerous different wireless communicationtechnologies and standards. Some examples of wireless communicationtechnologies include GSM, UMTS (associated with, for example, WCDMA orTD-SCDMA air interfaces), LTE, LTE Advanced (LTE-A), HSPA, 3GPP2CDMA2000 (e.g., 1×RTT, 1×EV-DO, HRPD, eHRPD), IEEE 802.11 (WLAN orWi-Fi), IEEE 802.16 (WiMAX), Bluetooth, and others.

Wireless communication can be useful for a wide breadth of deviceclasses, ranging from relatively simple (e.g., potentially inexpensive)devices which may have limited capabilities, to relatively complex(e.g., potentially more expensive) devices which may have greatercapabilities. Such devices may have different characteristics withrespect to processing, memory, battery, antenna (power/range,directionality), and/or other capabilities. Devices which exhibitrelatively limited reception and/or transmission capabilities (due todevice design, current transmission medium conditions, and/or otherfactors) may be referred to in some instances as “link budget limited”or “link budget constrained” devices.

SUMMARY

Embodiments are presented herein of apparatuses, systems, and methodsfor link budget limited devices to perform random access procedures.

Random access procedures (RACH procedures) between a wireless device anda base station may include exchanging a sequence of messages between thewireless device and the base station. At least in some instances, themessages may include a physical preamble (PRACH or MSG1), a randomaccess response (RAR or MSG2), a connection request (MSG3), and acontention resolution message (MSG4).

According to the techniques described herein, a base station may detectphysical preamble messages (MSG1s) transmitted by link budget limiteddevices using a different (e.g., lower) correlation threshold than isused for non-link budged limited devices. If a physical preamble messagecorresponding to a link budget limited device is detected, the basestation may select the MSG2 characteristics based on the device to whichthe MSG2 will be sent being link budget limited. For example, a highcontrol channel aggregation level may be used, the relevant controlchannel elements (CCEs) may be boosted in power, and/or a low modulationand coding scheme (possibly also with power boosting) may be selected.This may improve the likelihood that a link budget limited device (e.g.,which may lack receiver diversity, and/or may be at the cell edge) cansuccessfully receive the MSG2.

Furthermore, at least in some instances, the base station may indicateto such a link budget limited wireless device to utilize transmissioncharacteristics for the MSG3 based on the device being link budgetlimited. For example, the wireless device may be provided with a lowmodulation and coding scheme, and/or may be instructed to usetransmission time interval bundling (TTI-B) for the MSG3. As anotherpossibility, the wireless device may explicitly indicate that it is linkbudget constrained in the MSG3, if desired.

The techniques described herein may be implemented in and/or used with anumber of different types of devices, including but not limited tocellular base stations, cellular phones, tablet computers, wearablecomputing devices, portable media players, and any of various othercomputing devices.

This Summary is intended to provide a brief overview of some of thesubject matter described in this document. Accordingly, it will beappreciated that the above-described features are merely examples andshould not be construed to narrow the scope or spirit of the subjectmatter described herein in any way. Other features, aspects, andadvantages of the subject matter described herein will become apparentfrom the following Detailed Description, Figures, and Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present subject matter can be obtainedwhen the following detailed description of the embodiments is consideredin conjunction with the following drawings, in which:

FIG. 1 illustrates an exemplary (and simplified) wireless communicationsystem, according to some embodiments;

FIG. 2 illustrates a base station (BS) in communication with a userequipment (UE) device, according to some embodiments;

FIG. 3 illustrates an exemplary block diagram of a UE device, accordingto some embodiments;

FIG. 4 illustrates an exemplary block diagram of a BS, according to someembodiments;

FIG. 5 illustrates an exemplary random access procedure messagesequence, according to some embodiments;

FIG. 6 is a flowchart diagram illustrating an exemplary method foraccommodating link budget limited random access procedures, according tosome embodiments; and

FIG. 7 illustrates an exemplary radio resource control connectionrequest information element that could be used as part of a randomaccess procedure, according to some embodiments.

While the features described herein may be susceptible to variousmodifications and alternative forms, specific embodiments thereof areshown by way of example in the drawings and are herein described indetail. It should be understood, however, that the drawings and detaileddescription thereto are not intended to be limiting to the particularform disclosed, but on the contrary, the intention is to cover allmodifications, equivalents and alternatives falling within the spiritand scope of the subject matter as defined by the appended claims.

DETAILED DESCRIPTION Terms

The following is a glossary of terms used in this disclosure:

Memory Medium—Any of various types of non-transitory memory devices orstorage devices. The term “memory medium” is intended to include aninstallation medium, e.g., a CD-ROM, floppy disks, or tape device; acomputer system memory or random access memory such as DRAM, DDR RAM,SRAM, EDO RAM, Rambus RAM, etc.; a non-volatile memory such as a Flash,magnetic media, e.g., a hard drive, or optical storage; registers, orother similar types of memory elements, etc. The memory medium mayinclude other types of non-transitory memory as well or combinationsthereof. In addition, the memory medium may be located in a firstcomputer system in which the programs are executed, or may be located ina second different computer system which connects to the first computersystem over a network, such as the Internet. In the latter instance, thesecond computer system may provide program instructions to the firstcomputer for execution. The term “memory medium” may include two or morememory mediums which may reside in different locations, e.g., indifferent computer systems that are connected over a network. The memorymedium may store program instructions (e.g., embodied as computerprograms) that may be executed by one or more processors.

Carrier Medium—a memory medium as described above, as well as a physicaltransmission medium, such as a bus, network, and/or other physicaltransmission medium that conveys signals such as electrical,electromagnetic, or digital signals.

Programmable Hardware Element—includes various hardware devicescomprising multiple programmable function blocks connected via aprogrammable interconnect. Examples include FPGAs (Field ProgrammableGate Arrays), PLDs (Programmable Logic Devices), FPOAs (FieldProgrammable Object Arrays), and CPLDs (Complex PLDs). The programmablefunction blocks may range from fine grained (combinatorial logic or lookup tables) to coarse grained (arithmetic logic units or processorcores). A programmable hardware element may also be referred to as“reconfigurable logic”.

Computer System—any of various types of computing or processing systems,including a personal computer system (PC), mainframe computer system,workstation, network appliance, Internet appliance, personal digitalassistant (PDA), television system, grid computing system, or otherdevice or combinations of devices. In general, the term “computersystem” can be broadly defined to encompass any device (or combinationof devices) having at least one processor that executes instructionsfrom a memory medium.

User Equipment (UE) (or “UE Device”)—any of various types of computersystems devices which are mobile or portable and which performs wirelesscommunications. Examples of UE devices include mobile telephones orsmart phones (e.g., iPhone™, Android™-based phones), portable gamingdevices (e.g., Nintendo DS™, PlayStation Portable™, Gameboy Advance™,iPhone™), laptops, wearable devices (e.g., smart watch, smart glasses),PDAs, portable Internet devices, music players, data storage devices, orother handheld devices, etc. In general, the term “UE” or “UE device”can be broadly defined to encompass any electronic, computing, and/ortelecommunications device (or combination of devices) which is easilytransported by a user and capable of wireless communication.

Wireless Device—any of various types of computer system devices whichperforms wireless communications. A wireless device can be portable (ormobile) or may be stationary or fixed at a certain location. A UE is anexample of a wireless device.

Base Station—The term “Base Station” has the full breadth of itsordinary meaning, and at least includes a wireless communication stationinstalled at a fixed location and used to communicate as part of awireless telephone system or radio system.

Link Budget Limited—includes the full breadth of its ordinary meaning,and at least includes a characteristic of a wireless device (a UE) whichexhibits limited communication capabilities, or limited power, relativeto a device that is not link budget limited, or relative to devices forwhich a radio access technology (RAT) standard has been developed. A UEthat is link budget limited may experience relatively limited receptionand/or transmission capabilities, which may be due to one or morefactors such as device design, device size, battery size, antenna sizeor design, transmit power, receive power, current transmission mediumconditions, and/or other factors. Such devices may be referred to hereinas “link budget limited” (or “link budget constrained”) devices. Adevice may be inherently link budget limited due to its size, batterypower, and/or transmit/receive power. For example, a smart watch that iscommunicating over LTE or LTE-A with a base station may be inherentlylink budget limited due to its reduced transmit/receive power and/orreduced antenna. Wearable devices, such as smart watches, are generallylink budget limited devices. Alternatively, a device may not beinherently link budget limited, e.g., may have sufficient size, batterypower, and/or transmit/receive power for normal communications over LTEor LTE-A, but may be temporarily link budget limited due to currentcommunication conditions, e.g., a smart phone being at the edge of acell, etc. It is noted that the term “link budget limited” includes orencompasses power limitations, and thus a power limited device may beconsidered a link budget limited device.

Processing Element (or Processor)—refers to various elements orcombinations of elements. Processing elements include, for example,circuits such as an ASIC (Application Specific Integrated Circuit),portions or circuits of individual processor cores, entire processorcores, individual processors, programmable hardware devices such as afield programmable gate array (FPGA), and/or larger portions of systemsthat include multiple processors.

Channel—a medium used to convey information from a sender (transmitter)to a receiver. It should be noted that since characteristics of the term“channel” may differ according to different wireless protocols, the term“channel” as used herein may be considered as being used in a mannerthat is consistent with the standard of the type of device withreference to which the term is used. In some standards, channel widthsmay be variable (e.g., depending on device capability, band conditions,etc.). For example, LTE may support scalable channel bandwidths from 1.4MHz to 20 MHz. In contrast, WLAN channels may be 22 MHz wide whileBluetooth channels may be 1 Mhz wide. Other protocols and standards mayinclude different definitions of channels. Furthermore, some standardsmay define and use multiple types of channels, e.g., different channelsfor uplink or downlink and/or different channels for different uses suchas data, control information, etc.

Band—The term “band” has the full breadth of its ordinary meaning, andat least includes a section of spectrum (e.g., radio frequency spectrum)in which channels are used or set aside for the same purpose.

Automatically—refers to an action or operation performed by a computersystem (e.g., software executed by the computer system) or device (e.g.,circuitry, programmable hardware elements, ASICs, etc.), without userinput directly specifying or performing the action or operation. Thusthe term “automatically” is in contrast to an operation being manuallyperformed or specified by the user, where the user provides input todirectly perform the operation. An automatic procedure may be initiatedby input provided by the user, but the subsequent actions that areperformed “automatically” are not specified by the user, i.e., are notperformed “manually”, where the user specifies each action to perform.For example, a user filling out an electronic form by selecting eachfield and providing input specifying information (e.g., by typinginformation, selecting check boxes, radio selections, etc.) is fillingout the form manually, even though the computer system must update theform in response to the user actions. The form may be automaticallyfilled out by the computer system where the computer system (e.g.,software executing on the computer system) analyzes the fields of theform and fills in the form without any user input specifying the answersto the fields. As indicated above, the user may invoke the automaticfilling of the form, but is not involved in the actual filling of theform (e.g., the user is not manually specifying answers to fields butrather they are being automatically completed). The presentspecification provides various examples of operations beingautomatically performed in response to actions the user has taken.

FIGS. 1 and 2—Communication System

FIG. 1 illustrates an exemplary (and simplified) wireless communicationsystem, according to some embodiments. It is noted that the system ofFIG. 1 is merely one example of a possible system, and embodiments maybe implemented in any of various systems, as desired.

As shown, the exemplary wireless communication system includes a basestation 102A which communicates over a transmission medium with one ormore user devices 106A, 106B, etc., through 106N. Each of the userdevices may be referred to herein as a “user equipment” (UE). Thus, theuser devices 106 are referred to as UEs or UE devices.

The base station 102A may be a base transceiver station (BTS) or cellsite, and may include hardware that enables wireless communication withthe UEs 106A through 106N. The base station 102A may also be equipped tocommunicate with a network 100 (e.g., a core network of a cellularservice provider, a telecommunication network such as a public switchedtelephone network (PSTN), and/or the Internet, among variouspossibilities). Thus, the base station 102A may facilitate communicationbetween the user devices and/or between the user devices and the network100.

The communication area (or coverage area) of the base station may bereferred to as a “cell.” The base station 102A and the UEs 106 may beconfigured to communicate over the transmission medium using any ofvarious radio access technologies (RATs), also referred to as wirelesscommunication technologies, or telecommunication standards, such as GSM,UMTS (WCDMA, TD-SCDMA), LTE, LTE-Advanced (LTE-A), HSPA, 3GPP2 CDMA2000(e.g., 1×RTT, 1×EV-DO, HRPD, eHRPD), Wi-Fi, WiMAX etc.

Base station 102A and other similar base stations (such as base stations102B . . . 102N) operating according to the same or a different cellularcommunication standard may thus be provided as a network of cells, whichmay provide continuous or nearly continuous overlapping service to UEs106A-N and similar devices over a geographic area via one or morecellular communication standards.

Thus, while base station 102A may act as a “serving cell” for UEs 106A-Nas illustrated in FIG. 1, each UE device 106 may also be capable ofreceiving signals from (and possibly within communication range of) oneor more other cells (which might be provided by base stations 102B-Nand/or any other base stations), which may be referred to as“neighboring cells”. Such cells may also be capable of facilitatingcommunication between user devices and/or between user devices and thenetwork 100, according to the same wireless communication technology asbase station 102A and/or any of various other possible wirelesscommunication technologies. Such cells may include “macro” cells,“micro” cells, “pico” cells, and/or cells which provide any of variousother granularities of service area size. For example, base stations102A-B illustrated in FIG. 1 might be macro cells, while base station102N might be a micro cell. Other configurations are also possible.

Note that a UE 106 may be capable of communicating using multiplewireless communication standards. For example, a UE 106 may beconfigured to communicate using a wireless networking (e.g., Wi-Fi)and/or peer-to-peer wireless communication protocol (e.g., BT, Wi-Fipeer-to-peer, etc.) in addition to at least one cellular communicationprotocol (e.g., GSM, UMTS (WCDMA, TD-SCDMA), LTE, LTE-A, HSPA, 3GPP2CDMA2000 (e.g., 1×RTT, 1×EV-DO, HRPD, eHRPD), etc.). The UE 106 may alsoor alternatively be configured to communicate using one or more globalnavigational satellite systems (GNSS, e.g., GPS or GLONASS), one or moremobile television broadcasting standards (e.g., ATSC-M/H or DVB-H),and/or any other wireless communication protocol, if desired. Othercombinations of wireless communication standards (including more thantwo wireless communication standards) are also possible.

FIG. 2 illustrates user equipment 106 (e.g., one of the devices 106Athrough 106N) in communication with a base station 102 (e.g., one of thebase stations 102A through 102N), according to some embodiments. The UE106 may be a device with cellular communication capability such as amobile phone, a hand-held device, a wearable device, a computer or atablet, or virtually any type of wireless device.

The UE 106 may include a processor that is configured to execute programinstructions stored in memory. The UE 106 may perform any of the methodembodiments described herein by executing such stored instructions.Alternatively, or in addition, the UE 106 may include a programmablehardware element such as an FPGA (field-programmable gate array) that isconfigured to perform any of the method embodiments described herein, orany portion of any of the method embodiments described herein.

The UE 106 may include one or more antennas for communicating using oneor more wireless communication protocols or technologies. In someembodiments, the UE 106 might be configured to communicate using eitherof CDMA2000 (1×RTT/1×EV-DO/HRPD/eHRPD) or LTE using a single sharedradio and/or GSM or LTE using the single shared radio. The shared radiomay couple to a single antenna, or may couple to multiple antennas(e.g., for MIMO) for performing wireless communications. In general, aradio may include any combination of a baseband processor, analog RFsignal processing circuitry (e.g., including filters, mixers,oscillators, amplifiers, etc.), or digital processing circuitry (e.g.,for digital modulation as well as other digital processing). Similarly,the radio may implement one or more receive and transmit chains usingthe aforementioned hardware. For example, the UE 106 may share one ormore parts of a receive and/or transmit chain between multiple wirelesscommunication technologies, such as those discussed above.

In some embodiments, the UE 106 may include separate (and possiblymultiple) transmit and/or receive chains (e.g., including separate RFand/or digital radio components) for each wireless communicationprotocol with which it is configured to communicate. As a furtherpossibility, the UE 106 may include one or more radios which are sharedbetween multiple wireless communication protocols, and one or moreradios which are used exclusively by a single wireless communicationprotocol. For example, the UE 106 might include a shared radio forcommunicating using either of LTE or 1×RTT (or LTE or GSM), and separateradios for communicating using each of Wi-Fi and Bluetooth. Otherconfigurations are also possible.

FIG. 3—Exemplary Block Diagram of a UE Device

FIG. 3 illustrates an exemplary block diagram of a UE 106, according tosome embodiments. As shown, the UE 106 may include a system on chip(SOC) 300, which may include portions for various purposes. For example,as shown, the SOC 300 may include processor(s) 302, which may executeprogram instructions for the UE 106, and display circuitry 304, whichmay perform graphics processing and provide display signals to thedisplay 360. The processor(s) 302 may also be coupled to memorymanagement unit (MMU) 340, which may be configured to receive addressesfrom the processor(s) 302 and translate those addresses to locations inmemory (e.g., memory 306, read only memory (ROM) 350, NAND flash memory310) and/or to other circuits or devices, such as the display circuitry304, wireless communication circuitry 330, connector I/F 320, and/ordisplay 360. The MMU 340 may be configured to perform memory protectionand page table translation or set up. In some embodiments, the MMU 340may be included as a portion of the processor(s) 302.

As shown, the SOC 300 may be coupled to various other circuits of the UE106. For example, the UE 106 may include various types of memory (e.g.,including NAND flash 310), a connector interface 320 (e.g., for couplingto a computer system, dock, charging station, etc.), the display 360,and wireless communication circuitry 330 (e.g., for LTE, Wi-Fi, GPS,etc.).

The UE device 106 may include at least one antenna (and possiblymultiple antennas, e.g., for MIMO and/or for implementing differentwireless communication technologies, among various possibilities), forperforming wireless communication with base stations and/or otherdevices. For example, the UE device 106 may use antenna(s) 335 toperform the wireless communication. As noted above, the UE 106 may beconfigured to communicate wirelessly using multiple wirelesscommunication technologies in some embodiments.

As described further subsequently herein, the UE 106 may includehardware and software components for implementing features describedherein, such as those described herein with reference to, inter alia,FIG. 6. The processor 302 of the UE device 106 may be configured toimplement part or all of the methods described herein, e.g., byexecuting program instructions stored on a memory medium (e.g., anon-transitory computer-readable memory medium). In other embodiments,processor 302 may be configured as a programmable hardware element, suchas an FPGA (Field Programmable Gate Array), or as an ASIC (ApplicationSpecific Integrated Circuit). Alternatively (or in addition) theprocessor 302 of the UE device 106, in conjunction with one or more ofthe other components 300, 304, 306, 310, 320, 330, 335, 340, 350, 360may be configured to implement part or all of the features describedherein, such as the features described herein with reference to, interalia, FIG. 6.

FIG. 4—Exemplary Block Diagram of a Base Station

FIG. 4 illustrates an exemplary block diagram of a base station 102,according to some embodiments. It is noted that the base station of FIG.4 is merely one example of a possible base station. As shown, the basestation 102 may include processor(s) 404 which may execute programinstructions for the base station 102. The processor(s) 404 may also becoupled to memory management unit (MMU) 440, which may be configured toreceive addresses from the processor(s) 404 and translate thoseaddresses to locations in memory (e.g., memory 460 and read only memory(ROM) 450) or to other circuits or devices.

The base station 102 may include at least one network port 470. Thenetwork port 470 may be configured to couple to a telephone network andprovide a plurality of devices, such as UE devices 106, access to thetelephone network as described above in FIGS. 1 and 2.

The network port 470 (or an additional network port) may also oralternatively be configured to couple to a cellular network, e.g., acore network of a cellular service provider. The core network mayprovide mobility related services and/or other services to a pluralityof devices, such as UE devices 106. In some cases, the network port 470may couple to a telephone network via the core network, and/or the corenetwork may provide a telephone network (e.g., among other UE devicesserviced by the cellular service provider).

The base station 102 may include at least one antenna 434, and possiblymultiple antennas. The antenna(s) 434 may be configured to operate as awireless transceiver and may be further configured to communicate withUE devices 106 via radio 430. The antenna(s) 434 communicates with theradio 430 via communication chain 432. Communication chain 432 may be areceive chain, a transmit chain or both. The radio 430 may be configuredto communicate via various wireless telecommunication standards,including, but not limited to, LTE, LTE-A, UMTS, CDMA2000, Wi-Fi, etc.

The BS 102 may be configured to communicate wirelessly using multiplewireless communication standards. In some instances, the base station102 may include multiple radios, which may enable the base station 102to communicate according to multiple wireless communicationtechnologies. For example, as one possibility, the base station 102 mayinclude an LTE radio for performing communication according to LTE aswell as a Wi-Fi radio for performing communication according to Wi-Fi.In such a case, the base station 102 may be capable of operating as bothan LTE base station and a Wi-Fi access point. As another possibility,the base station 102 may include a multi-mode radio which is capable ofperforming communications according to any of multiple wirelesscommunication technologies (e.g., LTE and Wi-Fi).

The BS 102 may include hardware and software components for implementingor supporting implementation of features described herein, such as thosedescribed herein with reference to, inter alia, FIG. 6. The processor404 of the base station 102 may be configured to implement part or allof the methods described herein, e.g., by executing program instructionsstored on a memory medium (e.g., a non-transitory computer-readablememory medium). Alternatively, the processor 404 may be configured as aprogrammable hardware element, such as an FPGA (Field Programmable GateArray), or as an ASIC (Application Specific Integrated Circuit), or acombination thereof. Alternatively (or in addition) the processor 404 ofthe BS 102, in conjunction with one or more of the other components 430,432, 434, 440, 450, 460, 470 may be configured to implement or supportimplementation of part or all of the features described herein, such asthe features described herein with reference to, inter alia, FIG. 6.

FIG. 5—Exemplary RACH Procedure

In LTE, in order to initially register with a network and/or toestablish a radio resource control (RRC) connection to exchange data, awireless device may exchange a sequence of messages with a base stationusing a random access channel (RACH). Such a message exchange may alsobe referred to as a RACH procedure.

A RACH procedure may be a contention-based procedure for acquiringsynchronization and establishing communication channels and/or radiolinks that provide access to more extensive network resources (e.g.,data carrying channels and/or greater uplink/downlink bandwidth). Forexample, a UE may attempt to perform a RACH procedure in order to obtainan RRC connection, which may in turn be used to service an applicationdata request, at least as one possibility.

FIG. 5 is a signal flow diagram illustrating an exemplary RACH proceduresuch as might be performed between a UE 106 and a base station 102according to LTE. It should be noted while the exemplary detailsillustrated in and described with respect to FIG. 5 may berepresentative of one possible technique for initially attaching to anetwork and/or transitioning to connected mode, other techniques (e.g.,according to other RATs) are also possible. Accordingly, the features ofFIG. 5 are not intended to be limiting to the disclosure as a whole:numerous variations and alternatives to the details provided hereinbelow are possible and should be considered within the scope of thedisclosure.

As shown, in 502 the UE 106 may transmit a first message to the basestation 102. The first message (“Msg1”) may include a physical RACH(PRACH) preamble, which may function as or indicate a random accessradio network temporary identifier (RA-RNTI). In some embodiments, thePRACH preamble may include one or more Zadoff-Chu (ZC) sequences, whichthe base station may detect using a correlation receiver.

In 504, the UE 106 may receive a second message from the base station102. The second message (“Msg2”, also referred to as “random accessresponse” or “RAR”) may include a timing advance (TA) parameter, atemporary cell radio network temporary identifier (TC-RNTI), and anuplink grant for transmitting a third message.

In 506, the UE 106 may transmit the third message to the base station102. The third message (“Msg3”, also referred to as “RRC connectionrequest”) may include the TC-RNTI and a system architecture evolutiontemporary mobile subscriber identity (S-TMSI) to identify the UE 106 tothe base station 102.

In 508, the UE 106 may receive a fourth message from the base station102. The fourth message (“Msg4” or “contention resolution message”) maypromote the TC-RNTI to a cell radio network temporary identifier(C-RNTI). The C-RNTI may be used for subsequent connected-mode RACHprocedure attempts, among various uses, as desired.

Upon completion of the four message sequence, the UE 106 may be in aconnected mode (e.g., RRC_connected) with the base station 102, and mayperform network data exchange via its serving cell.

FIG. 6—Flowchart

As previously noted herein, a wireless device may attempt to perform aRACH procedure with a base station to initially register with a networkand/or to establish a RRC connection with the base station providing aserving cell. Accordingly, in order to facilitate cell access by devices(e.g., range constrained devices and/or those in poor RF conditions)that have limited link budgets, particularly as demand grows forinexpensive and limited capability devices, it may be desirable toprovide mechanisms to improve the abilities of such devices to succeedwhen attempting to perform a RACH procedure.

FIG. 6 is a flowchart diagram illustrating a method for a base stationto detect when a link budget constrained wireless device is attemptingto perform a RACH procedure, and to select characteristics of follow upmessages based on this information, which may improve the chances ofsuccess for a RACH procedure by the link budget constrained wirelessdevice. Note that while elements of the method of FIG. 6 are describedsubstantially with reference to the LTE wireless communicationtechnology, part or all of the method may be used in conjunction withother wireless communication technologies, as desired.

The method shown in FIG. 6 may be used in conjunction with any of thecomputer systems or devices shown in the above Figures, among otherdevices. In various embodiments, some of the elements shown may beperformed concurrently, in a different order than shown, substituted forby other elements, or may be omitted. Additional elements may also beperformed as desired. As shown, the method may operate as follows.

In 602, the base station may detect a PRACH preamble from a link budgetconstrained wireless device. As previously noted with respect to FIG. 5herein, a PRACH preamble (or simply “PRACH”) may, at least in someinstances, include a ZC sequence. The base station may include acorrelation receiver and may use any of various detection algorithms fordetecting PRACH signals received by the base station. For example, ZCcross-correlation may be used to determine a signal's correlation levelin order to perform Msg1 detection.

If a link budget limited wireless device transmits a PRACH, it may bethe case that the PRACH correlation level is lower than PRACHs receivedfrom non-link budget limited devices. For example, link budgetlimitations may result from hardware limitations (e.g., power amplifierand/or antenna limitations, lack of receive diversity, etc.) and/or RFconditions (e.g., if the wireless device is at cell edge, in a shieldedlocation, etc.) that may result in signals from such a device beingreceived by the base station with lower signal strength (which mayresult in lower correlation level) than signals from other devices.

Thus, as one possibility for detecting that a PRACH is received from alink budget constrained wireless device, the base station may utilizemultiple correlation thresholds for detecting incoming PRACHs. Forexample, incoming signals that meet a first (e.g., higher) correlationthreshold may be determined to be received from devices which are notlink budget limited, while incoming signals that do not meet the firstcorrelation threshold but do meet a second (e.g., lower) correlationthreshold may be determined to be received from devices which are linkbudget limited. Signals that fall below the second threshold may bedetermined to not correspond to incoming PRACHs (e.g., may be backgroundnoise and/or interference), and wireless devices transmitting suchsignals may not be detected.

Note that the correlation thresholds may be selected as desired. As onepossibility, the first threshold may be selected to provideapproximately (or less than) 1% probability of missed detection (PMD)and approximately (or less than) 0.1% probability of false alarm (PFA).

In 604, the base station may select PRACH responseparameters/characteristics based on detecting that the PRACH is receivedfrom a link budget constrained wireless device. The PRACH responseparameters may be associated with a message sent by the base station inresponse to the PRACH (e.g., the Msg2/RAR to be sent by the basestation) and/or a subsequent message from the link budget constrainedwireless device to the base station (e.g., the Msg3/RRC ConnectionRequest). For example, in some embodiments, the base station mayallocate and assign more resources to both the Msg2 and Msg3 if a linkbudget constrained Msg1 is detected, to improve the probability ofcorrect detection of those messages.

The Msg2 parameters/characteristics may relate to either or both of acontrol channel (e.g., physical downlink control channel or PDCCH inLTE) and a data channel (e.g., physical downlink shared channel or PDSCHin LTE). For example, a control channel format and/or aggregation levelmay be selected based on detecting that the PRACH is received from alink budget constrained wireless device. Using a higher (e.g., maximum)aggregation level (e.g., format 3/aggregation level 8 in LTE, as onepossibility) may increase the probability of a wireless device beingable to decode the control channel. Additionally, or alternatively, thebase station may boost the power for the relevant control channelelements (CCEs) of the control channel. As a still further possibility,the base station may select a low (e.g., the lowest possible) modulationand coding scheme (MCS) for the data channel on which the Msg2 istransmitted, possibly also with power boosting.

The Msg3 parameter(s)/characteristic(s) selected based on the PRACHbeing received from a link budget constrained wireless device may alsoinclude a MCS allocation. For example, a low (e.g., the lowest possible)MCS grant may be provided for the Msg3 for a link budget constrainedwireless device. Additionally, or alternatively, the base station maydetermine that the link budget constrained wireless device shouldimplement transmission time interval bundling (TTI-B) for the Msg3. Suchparameter(s)/characteristic(s) may be indicated to the link budgetconstrained wireless device by the base station as part of the Msg2transmitted by the base station, using any of a variety of possiblesignaling techniques. As one possibility, certain TC-RNTI values may bedesignated (e.g., specified in standard documents, and/or agreed upon byinfrastructure and device vendors) for use with link budget limiteddevices, such that use of those TC-RNTI values is understood to specifythe use of certain techniques such as TTI-B (e.g., at least for theMsg3). A base station could thus provide such a TC-RNTI in its Msg2/RARto a wireless device that has been determined to be link budgetconstrained, based on which the wireless device may subsequently useTTI-B (and/or other specified techniques). Alternatively (or inaddition), such parameter(s)/characteristic(s) may be indicated usingRRC information elements (IEs) and/or media access control (MAC) controlelements (CEs), among various possibilities.

As previously noted herein, link budget constraints may arise for any ofmultiple possible reasons. In some instances, the base station may beable to distinguish between different link budget constraint use-cases,and may further refine the RACH procedure parameter(s)/characteristic(s)selected depending on the reason a wireless device is link budgetconstrained.

For example, the base station may be able to compute the time of arrival(ToA) or round trip delay (RTD) for a wireless device based on the lagin the cross-correlation of the ZC sequence of a detected PRACHpreamble. This may in turn allow the base station to determine if thewireless device is in a cell-edge scenario (e.g., if the ToA is laterand/or RTD is larger than an associated threshold) or not (e.g., if theToA is earlier and/or RTD is smaller than an associated threshold).

The base station may refine the RACH procedureparameter(s)/characteristic(s) selected depending on the reason awireless device is link budget constrained in any of various manners. Asone possibility, the base station may make fewer/weaker accommodationsfor a wireless device in a cell-edge scenario than for a hardwareconstrained wireless device, for example since (at least in someinstances) a device at cell edge may be only temporarily link budgetlimited (and thus may be able to successfully perform a RACH procedureat least some of the time even if no accommodation is made) while ahardware constrained wireless device may be permanently link budgetlimited.

In 606, the base station may respond to the link budget constrainedPRACH preamble according to the selected parameters. This may includetransmitting the Msg2 using the parameter(s)/characteristic(s) selectedfor the Msg2, and/or indicating to the link budget constrained wirelessdevice via the Msg2 of the parameter(s)/characteristic(s) selected forthe link budget constrained wireless device to use with its Msg3. Thewireless device may further follow up by utilizing the indicatedparameters (e.g., MCS allocation, TTI-B if enabled, etc.) whentransmitting the Msg3 to the base station.

Note additionally that, at least in some instances, a link budgetconstrained wireless device may explicitly indicate that it is “linkbudget constrained” in its RRC connection request, for example using aRRC IE and/or a MAC CE. Alternatively or additionally, such anindication may encompass additional characteristics in addition to linkbudget limitations; for example, an indication of a device class orcategory (e.g., LTE category 0 devices (or categories 0-1, among variousother possibilities), which may be lower complexity, lower performance,and/or lower capability devices relative to other LTE categories) may beindicated with/as part of the RRC connection request, if desired. Thismay allow the base station (and more generally the network to which thebase station belongs) to select further/future communicationcharacteristics with a link budget constrained wireless device that areappropriate to the device in view of its link budget constraints and/orother characteristics.

FIG. 7—Exemplary RRC Connection Request Information Element Format

FIG. 7 illustrates an exemplary RRC connection request IE format thatmay be used by a wireless user equipment (UE) device, according to someembodiments. It should be noted while the exemplary details illustratedin and described with respect to FIG. 7 may be representative of onepossible IE format for a RRC connection request IE, other formats arealso possible. Accordingly, the features of FIG. 7 are not intended tobe limiting to the disclosure as a whole: numerous variations andalternatives to the details provided herein below are possible andshould be considered within the scope of the disclosure.

As shown, the message may include a “ue-Identity” field in whichidentification information for the UE, such as a S-TMSI, may beprovided. As another possibility, a random value may be used in thisfield.

As shown, the message may also include an “establishmentCause” field inwhich a reason for attempting to establish a RRC connection may beprovided. The values of the “establishmentCause” field may beenumerated, and may include emergency, highPriorityAccess, mt-Access,mo-Signaling, mo-Data, spare3, spare2, and spare1.

As one possibility for explicitly indicating that a UE is link budgetlimited, a special value in the random value field may be used toindicate that a UE is link budget limited. As another possibility, one(or more) of the spare values in the establishmentCause field may beused to indicate that a UE is link budget limited. For example, as onepossibility, the spare3 value could be used to indicate “mt-Access+linkbudget constrained”, the spare2 value could be used to indicate“mo-Signaling+link budget constrained”, and the spare1 value could beused to indicate “mo-Data+link budget constrained”.

In the following further exemplary embodiments are provided.

One set of embodiments may include a method for a base stationconfigured to serve a cell, comprising: by the base station: detecting apreamble message on a physical random access channel; determining thatthe preamble message is received from a link budget constrained wirelessdevice; selecting characteristics of a response message based ondetermining that the preamble message is received from a link budgetconstrained wireless device; and transmitting the response message tothe link budget constrained wireless device using the selectedcharacteristics.

According to some embodiments, wherein determining that the preamblemessage is received from a link budget constrained wireless devicecomprises determining that the preamble message does not meet a firstcorrelation threshold and does meet a second correlation, wherein thefirst correlation threshold is higher than the second correlationthreshold.

According to some embodiments, the characteristics of the responsemessage are selected to increase the robustness of the response message.

According to some embodiments, the characteristics of the responsemessage comprise one or more of: an aggregation level of a controlchannel; a power level of control channel elements associated with theresponse message; or a modulation and coding scheme of the responsemessage.

According to some embodiments, the characteristics of the responsemessage are selected to increase the robustness of a subsequent messagefrom the link budget constrained wireless device to the base station.

According to some embodiments, the characteristics of the responsemessage comprise one or more of: a modulation and coding scheme grantfor the subsequent message from the link budget constrained wirelessdevice; or an indication to use transmission time interval bundling forthe subsequent message from the link budget constrained wireless device.

A further set of embodiments may include a base station configured toserve a cell, comprising: a radio; and a processing element operablycoupled to the radio, wherein the processing element and the radio areconfigured to implement any or all parts of any of the preceding methodfor a base station.

A further exemplary embodiment may include a method for a wirelessdevice, the method comprising: by the wireless device: transmitting apreamble message to a base station on a physical random access channel;receiving a random access response message from the base station; andtransmitting a radio resource control connection request usinginformation from the random access response message, wherein the radioresource control connection request indicates that the wireless deviceis link budget constrained.

According to some embodiments, the random access response messageindicates to use transmission time interval bundling for the radioresource control connection request, wherein transmitting the radioresource control connection request uses transmission time intervalbundling.

Yet another exemplary embodiment may include a wireless device,comprising: a radio; and a processing element operably coupled to theradio, wherein the processing element and the radio are configured toimplement any or all parts of the preceding method for a wirelessdevice.

A further exemplary set of embodiments may include a non-transitorycomputer accessible memory medium comprising program instructions which,when executed at a device, cause the device to implement any or allparts of any of the preceding examples.

A still further exemplary set of embodiments may include a computerprogram comprising instructions for performing any or all parts of anyof the preceding examples.

Yet another exemplary set of embodiments may include an apparatuscomprising means for performing any or all of the elements of any of thepreceding examples.

Embodiments of the present disclosure may be realized in any of variousforms. For example some embodiments may be realized as acomputer-implemented method, a computer-readable memory medium, or acomputer system. Other embodiments may be realized using one or morecustom-designed hardware devices such as ASICs. Still other embodimentsmay be realized using one or more programmable hardware elements such asFPGAs.

In some embodiments, a non-transitory computer-readable memory mediummay be configured so that it stores program instructions and/or data,where the program instructions, if executed by a computer system, causethe computer system to perform a method, e.g., any of a methodembodiments described herein, or, any combination of the methodembodiments described herein, or, any subset of any of the methodembodiments described herein, or, any combination of such subsets.

In some embodiments, a device (e.g., a UE 106) may be configured toinclude a processor (or a set of processors) and a memory medium, wherethe memory medium stores program instructions, where the processor isconfigured to read and execute the program instructions from the memorymedium, where the program instructions are executable to implement anyof the various method embodiments described herein (or, any combinationof the method embodiments described herein, or, any subset of any of themethod embodiments described herein, or, any combination of suchsubsets). The device may be realized in any of various forms.

Although the embodiments above have been described in considerabledetail, numerous variations and modifications will become apparent tothose skilled in the art once the above disclosure is fully appreciated.It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

What is claimed is:
 1. A method for a base station configured to serve acell, comprising: by the base station: detecting a preamble message on aphysical random access channel; determining that the preamble message isreceived from a link budget constrained wireless device, whereindetermining that the preamble message is received from the link budgetconstrained wireless device comprises determining that the preamblemessage does not meet a first correlation threshold and does meet asecond correlation threshold, wherein the first correlation threshold ishigher than the second correlation threshold; selecting characteristicsof a response message based at least in part on determining that thepreamble message is received from the link budget constrained wirelessdevice; and transmitting the response message to the link budgetconstrained wireless device using the selected characteristics.
 2. Themethod of claim 1, wherein the characteristics of the response messageare selected to increase the robustness of the response message.
 3. Themethod of claim 1, wherein the characteristics of the response messagecomprise one or more of: an aggregation level of a control channel onwhich the response message is transmitted; a power level of controlchannel elements associated with the response message; or a modulationand coding scheme of the response message.
 4. The method of claim 1,wherein the characteristics of the response message are selected toincrease the robustness of a subsequent message from the link budgetconstrained wireless device to the base station.
 5. The method of claim1, wherein the characteristics of the response message comprise one ormore of: a modulation and coding scheme grant for a subsequent messagefrom the link budget constrained wireless device; or an indication touse transmission time interval bundling for the subsequent message fromthe link budget constrained wireless device.
 6. The method of claim 1,further comprising: determining whether the link budget constraineddevice is ata cell edge based on one or more of time of arrival or roundtrip delay of the preamble message, wherein the characteristics of theresponse message are selected further based on whether the link budgetconstrained device is at the cell edge.
 7. A base station configured toserve a cell, comprising: a radio; and a processing element operablycoupled to the radio, wherein the processing element and the radio areconfigured to: determine that a preamble message received from awireless user equipment (UE) device on a physical random access channeldoes not meet a first correlation threshold and does meet a secondcorrelation threshold, wherein the first correlation threshold is higherthan the second correlation threshold; select characteristics of aresponse message transmitted to the UE device based on determining thatthe preamble message is does not meet the first correlation thresholdand does meet the second correlation threshold; and transmit theresponse message to the UE device using the selected characteristics. 8.The base station of claim 7, wherein to select the characteristics ofthe response message, the processing element and the radio are furtherconfigured to select an aggregation level of a control channel on whichthe response message is transmitted, wherein a higher aggregation levelis selected based on the preamble message not meeting the firstcorrelation threshold than if the preamble message met the firstcorrelation threshold.
 9. The base station of claim 7, wherein to selectthe characteristics of the response message, the processing element andthe radio are further configured to select a power level of controlchannel elements associated with the response message, wherein a higherpower level is selected based on the preamble message not meeting thefirst correlation threshold than if the preamble message met the firstcorrelation threshold.
 10. The base station of claim 7, wherein toselect the characteristics of the response message, the processingelement and the radio are further configured to select a modulation andcoding scheme of the response message, wherein a lower modulation andcoding scheme is selected based on the preamble message not meeting thefirst correlation threshold than if the preamble message met the firstcorrelation threshold.
 11. The base station of claim 7, wherein theresponse message comprises an indication of a modulation and codingscheme grant for a connection request message to be transmitted by theUE device, wherein to select the characteristics of the responsemessage, the processing element and the radio are further configured toselect the modulation and coding scheme grant, wherein a lowermodulation and coding scheme grant is selected based on the preamblemessage not meeting the first correlation threshold than if the preamblemessage met the first correlation threshold.
 12. The base station ofclaim 7, wherein to select the characteristics of the response message,the processing element and the radio are further configured to select toprovide an indication to use transmission time interval bundling for aconnection request message to be transmitted by the UE device based onthe preamble message not meeting the first correlation threshold. 13.The base station of claim 7, wherein the processing element and theradio are further configured to: receive an indication in a connectionrequest message received from the UE device that the UE device is linkbudget constrained; and select further communication characteristicswith the UE device based at least in part on the indication that the UEdevice is link budget constrained.
 14. The base station of claim 7,wherein the processing element and the radio are further configured to:estimate whether the preamble message does not meet the firstcorrelation threshold because the UE device is at a cell edge or becausethe UE device is hardware constrained based at least in part on lag incross-correlation of the preamble message.
 15. An apparatus configuredfor implementation in a base station configured to serve a cell,comprising: one or more processing elements, wherein the one or moreprocessing elements are configured to: determine that a preamble messagereceived from a wireless user equipment (UE) device on a physical randomaccess channel does not meet a first correlation threshold and does meeta second correlation threshold, wherein the first correlation thresholdis higher than the second correlation threshold; select characteristicsof a response message transmitted to the UE device based on determiningthat the preamble message is does not meet the first correlationthreshold and does meet the second correlation threshold; and transmitthe response message to the UE device using the selectedcharacteristics.
 16. The apparatus of claim 15, wherein to select thecharacteristics of the response message, the one or more processingelements are further configured to select an aggregation level of acontrol channel on which the response message is transmitted, wherein ahigher aggregation level is selected based on the preamble message notmeeting the first correlation threshold than if the preamble message metthe first correlation threshold.
 17. The apparatus of claim 15, whereinto select the characteristics of the response message, the one or moreprocessing elements are further configured to select a power level ofcontrol channel elements associated with the response message, wherein ahigher power level is selected based on the preamble message not meetingthe first correlation threshold than if the preamble message met thefirst correlation threshold.
 18. The apparatus of claim 15, wherein toselect the characteristics of the response message, the one or moreprocessing elements are further configured to select a modulation andcoding scheme of the response message, wherein a lower modulation andcoding scheme is selected based on the preamble message not meeting thefirst correlation threshold than if the preamble message met the firstcorrelation threshold.
 19. The apparatus of claim 15, wherein to selectthe characteristics of the response message, the one or more processingelements are further configured to select to provide an indication touse transmission time interval bundling for a connection request messageto be transmitted by the UE device based on the preamble message notmeeting the first correlation threshold.
 20. The apparatus of claim 15,wherein the one or more processing elements are further configured to:estimate whether the preamble message does not meet the firstcorrelation threshold because the UE device is at a cell edge or becausethe UE device is hardware constrained based at least in part on lag incross-correlation of the preamble message, wherein said selecting thecharacteristics of the response message is based on the UE device beingat the cell edge or being hardware constrained.